Reinforced high strength microwave antenna

ABSTRACT

A microwave antenna has a radiating portion connected by a feedline to a power generating source, e.g., a generator. Proximal and distal radiating portions of the antenna assembly are separated by a junction member. A reinforcing member is disposed within the junction member to increase structural rigidity.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 14/153,644, filed on Jan. 13, 2014, which is acontinuation application of U.S. patent application Ser. No. 13/479,588,filed on May 24, 2012, now U.S. Pat. No. 8,663,213, which is acontinuation application of U.S. patent application Ser. No. 13/214,503,filed on Aug. 22, 2011, now U.S. Pat. No. 8,192,423, which is acontinuation application of U.S. patent application Ser. No. 12/859,841,filed on Aug. 20, 2010, now U.S. Pat. No. 8,012,148, which is acontinuation application of U.S. patent application Ser. No. 11/126,531,now U.S. Pat. No. 7,799,019, filed on May 10, 2005, the entire contentsof each of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The described devices relate generally to microwave antenna probes andmethods of their use, e.g., in tissue ablation applications. Moreparticularly, the described devices relate to microwave antennas thatmay be inserted directly into tissue for diagnosis and treatment ofdiseases.

2. Background of Related Art

In the treatment of diseases such as cancer, certain types of cancercells have been found to denature at elevated temperatures (which areslightly lower than temperatures normally injurious to healthy cells).These types of treatments, known generally as hyperthermia therapy,typically utilize electromagnetic radiation to heat diseased cells totemperatures above 41° C. while maintaining adjacent healthy cells atlower temperatures where irreversible cell destruction will not occur.Other procedures utilizing electromagnetic radiation to heat tissue alsoinclude ablation and coagulation of the tissue. Such microwave ablationprocedures, e.g., such as those performed for menorrhagia, are typicallydone to ablate and coagulate the targeted tissue to denature or kill it.Many procedures and types of devices utilizing electromagnetic radiationtherapy are known in the art. Such microwave therapy is typically usedin the treatment of tissue and organs such as the prostate, heart, andliver.

One non-invasive procedure generally involves the treatment of tissue(e.g., a tumor) underlying the skin via the use of microwave energy. Themicrowave energy is able to non-invasively penetrate the skin to reachthe underlying tissue. However, this non-invasive procedure may resultin the unwanted heating of healthy tissue. Thus, the non-invasive use ofmicrowave energy requires a great deal of control. This is partly why amore direct and precise method of applying microwave radiation has beensought.

Presently, there are several types of microwave probes in use, e.g.,monopole, dipole, and helical. One type is a monopole antenna probe,which consists of a single, elongated microwave conductor exposed at theend of the probe. The probe is sometimes surrounded by a dielectricsleeve. The second type of microwave probe commonly used is a dipoleantenna, which consists of a coaxial construction having an innerconductor and an outer conductor with a dielectric separating a portionof the inner conductor and a portion of the outer conductor. In themonopole and dipole antenna probe, microwave energy generally radiatesperpendicularly from the axis of the conductor.

The typical microwave antenna has a long, thin inner conductor whichextends along the axis of the probe and is surrounded by a dielectricmaterial and is further surrounded by an outer conductor around thedielectric material such that the outer conductor also extends along theaxis of the probe. In another variation of the probe, which provides foreffective outward radiation of energy or heating, a portion or portionsof the outer conductor can be selectively removed. This type ofconstruction is typically referred to as a “leaky waveguide” or “leakycoaxial” antenna. Another variation on the microwave probe involveshaving the tip formed in a uniform spiral pattern, such as a helix, toprovide the necessary configuration for effective radiation. Thisvariation can be used to direct energy in a particular direction, e.g.,perpendicular to the axis, in a forward direction (i.e., towards thedistal end of the antenna), or a combination thereof.

Invasive procedures and devices have been developed in which a microwaveantenna probe may be either inserted directly into a point of treatmentvia a normal body orifice or percutaneously inserted. Such invasiveprocedures and devices potentially provide better temperature control ofthe tissue being treated. Because of the small difference between thetemperature required for denaturing malignant cells and the temperatureinjurious to healthy cells, a known heating pattern and predictabletemperature control is important so that heating is confined to thetissue to be treated. For instance, hyperthermia treatment at thethreshold temperature of about 41.5° C. generally has little effect onmost malignant growth of cells. However, at slightly elevatedtemperatures above the approximate range of 43° C. to 45° C., thermaldamage to most types of normal cells is routinely observed. Accordingly,great care must be taken not to exceed these temperatures in healthytissue.

However, many types of malignancies are difficult to reach and treatusing non-invasive techniques or by using invasive antenna probesdesigned to be inserted into a normal body orifice, i.e., an easilyaccessible body opening. These types of conventional probes may be moreflexible and may also avoid the need to separately sterilize the probe;however, they are structurally weak and typically require the use of anintroducer or catheter to gain access to within the body. Moreover, theaddition of introducers and catheters necessarily increase the diameterof the incision or access opening into the body thereby making the useof such probes more invasive and further increasing the probability ofany complications that may arise.

Structurally stronger invasive probes exist and are typically long,narrow, needle-like antenna probes which may be inserted directly intothe body tissue to directly access a site of a tumor or othermalignancy. Such rigid probes generally have small diameters that aidnot only in ease of use but also reduce the resulting trauma to thepatient. A convenience of rigid antenna probes capable of directinsertion into tissue is that the probes may also allow for alternateadditional uses given different situations. However, such rigid,needle-like probes may experience difficulties in failing to provideuniform patterns of radiated energy; and may fail to provide uniformheating axially along and radially around an effective length of theprobe. Accordingly, it may be difficult to otherwise control and directthe heating pattern when using such probes.

Accordingly, there remains a need for a microwave antenna probe that mayhelp in overcoming the problems discussed above. There also exists aneed for a microwave antenna probe that is structurally robust enoughfor direct insertion into tissue without the need for additionalintroducers or catheters while producing a controllable and predictableheating pattern.

SUMMARY

The described methods and devices provide for microwave antenna probesand their method of use, e.g., in tissue ablation applications. In somevariations, the microwave antenna assembly has proximal and distalradiating portions. An inner and an outer conductor extend through theproximal radiating portion, with the inner conductor disposed within theouter conductor. The inner conductor further extends at least partiallyinto the distal radiating portion. A junction member separates theproximal and distal radiation sections with at least a portion of thejunction member disposed between the proximal and distal radiatingportions. A reinforcing member is disposed longitudinally at leastpartially within the junction member and provides additional stiffnessto the junction member, thereby increasing the overall structuralintegrity of the assembly and allowing for easier direct insertion ofthe assembly into tissue. The microwave antenna assembly may alsocomprise a sensor selected from the group consisting of a temperaturesensor, a pressure sensor, and a flow sensor. In some variations, thesensor is a temperature sensor. Methods for assembling the disclosedmicrowave antenna assemblies are also described.

In certain variations, the reinforcing member extends from the junctionmember into the distal radiating portion. In other variations, the innerconductor extends through the reinforcing member. The inner conductorcan be affixed to the distal radiating portion or can otherwise beplaced into electrical communication with the distal radiating portion.In yet other variations, the reinforcing member itself can be integrallyformed with the inner conductor as a single piece. In furthervariations, the inner conductor and distal radiating portion itself areintegrally formed as a single piece. The proximal radiating portion mayalso be a single piece, and in some variations, the proximal radiatingportion has a variable wall thickness. The microwave antenna assemblymay also be connected to a source of microwave energy.

In another variation the microwave antenna assembly is further providedwith a thermocouple for localized temperature sensing, with thethermocouple junction being positioned e.g., along the distal radiatingportion. In yet a further variation, the microwave assembly is furtherprovided with a lumen extending through at least a portion of theproximal radiating portion, or proximal to the proximal radiatingportion, and opening to the surface of the assembly, for e.g., todeliver therapeutic agents to tissue, to provide a thermocouple or othertemperature sensor, to act as an aspiration port for delivery or removalof fluids, or for the delivery of transducers or sensors to measure orsense various characteristics of the surrounding tissue and/or antennaperformance.

To improve the energy focus of the antenna assembly, an electrical chokemay also be used in any of the variations described herein to containreturning currents to the distal end of the antenna assembly. The chokemay be disposed on top of a dielectric material on the antenna proximalof the radiating section. The choke is preferably comprised of aconductive layer and may be further covered by a tubing or coating toforce the conductive layer to conform to the underlying antenna.

Additionally, variations on the choke, the tubing or coating, anysealant layers, as well as other layers that may be disposed over theantenna assembly may be used. Certain layers, e.g., a heatshrink layerdisposed over the antenna assembly, may have wires or strands integratedwithin the layer to further strengthen the antenna assembly. Kevlarwires, for instance, may be integrally formed into the layer andoriented longitudinally with the antenna axis to provide additionalstrength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a representative diagram of a variation of a microwaveantenna assembly described herein;

FIGS. 2A and 2B depict cross-sectional views of a conventional microwaveantenna assembly;

FIG. 3A depicts a side sectional view of a microwave antenna assemblyshowing a junction member and reinforcing member according to onevariation of the assemblies described herein;

FIG. 3B depicts a cross-sectional view of the assembly of FIG. 3A takenalong the plane designated by line 3B-3B;

FIGS. 4A and 4B depict side and perspective sectional views,respectively, of a microwave antenna assembly showing a junction memberand reinforcing member according to another variation of the describedmicrowave antenna assemblies;

FIG. 5 depicts a cross-sectional view of a microwave antenna assemblyshowing a junction member and reinforcing member according to yetanother variation of the microwave antenna assemblies described herein;

FIG. 6A depicts a cross-sectional view of a microwave antenna assemblyshowing a junction member and a reinforcing member according to afurther variation of the microwave antenna assemblies described herein;

FIGS. 6B and 6C depict enlarged cross-sectional views of the distal endand proximal section, respectively, of the microwave antenna assembly ofFIG. 6A;

FIG. 7 depicts a cross-sectional view of a microwave antenna assemblyshowing a cooling chamber according to a further variation of themicrowave antenna assemblies described herein; and

FIG. 8 depicts a cross-sectional view of a microwave antenna assemblywithout threaded mating sections adjacent to the junction member.

DETAILED DESCRIPTION

During invasive treatment of diseased areas of tissue in a patient,trauma may be caused to the patient resulting in pain and othercomplications. Various microwave antenna assemblies, as describedherein, are less traumatic than devices currently available and asdescribed in further detail below, methods of manufacturing such devicesare also described. Generally, the devices and assemblies described hereallow for the direct insertion of a microwave antenna into tissue forthe purposes of diagnosis and treatment of disease. FIG. 1 shows arepresentative diagram of a variation of a microwave antenna assembly10. The antenna assembly 10 is generally comprised of radiating portion12 that may be connected by shaft 14 via cable 15 to connector 16, whichmay further connect the assembly 10 to a power generating source 28,e.g., a generator or source of microwave energy. Assembly 10, as shown,is a dipole microwave antenna assembly, but other antenna assemblies,e.g., monopole helical, or leaky wave antenna assemblies, may alsoutilize the principles set forth herein. Distal portion 20 of radiatingportion 12 preferably has a tapered end 24 that terminates at a tip 26to allow for insertion into tissue with minimal resistance. In thosecases where the radiating portion 12 is inserted into a pre-existingopening, tip 26 may be rounded or flat.

In certain applications, a microwave antenna requires adequatestructural strength to prevent bending of the antenna, e.g., where theantenna is directly inserted into tissue, where the antenna undergoesbending moments after insertion, etc. FIGS. 2A and 2B show an end viewand a cross-sectional view, respectively, of a conventional dipolemicrowave antenna assembly 30. As seen, antenna assembly 30 has aproximal end 32 that may be connected to a shaft 14, as furtherdiscussed herein, and terminates at distal end 34. The radiating portionof antenna 30 comprises proximal radiating portion 36 and distalradiating portion 38. Proximal radiating portion 36 may typically havean outer conductor 42 and an inner conductor 44, each of which extendsalong a longitudinal axis. Between the outer and inner conductors 42 and44 is typically a dielectric material 46, which is also disposedlongitudinally between the conductors 42 and 44 to electrically separatethem. A dielectric material may constitute any suitable dielectricmaterial, including air. Distal portion 48 is also made from aconductive material, as discussed below. Proximal and distal radiatingportions 36 and 38 align at junction 40, which is typically made of adielectric material, and are also supported by inner conductor 44, whichruns through junction opening 50 and at least partially through distalportion 48. The construction of conventional antenna assembly 30however, is structurally weak at junction 40.

Accordingly, there are various configurations designed to increase theantenna strength. Such configurations include those described in U.S.Pat. No. 6,878,147 filed Nov. 2, 2001, which is incorporated herein byreference in its entirety. One configuration involves placing theantenna assembly under a compressive load to stiffen the radiatingportions. Another configuration involves mechanically fastening, e.g.,in a screw-like manner, the radiating portions together to provide ajoint that will withstand bending moments. A further configurationinvolves creating overlapping joints between the radiating portions ofthe antenna assembly to provide a high-strength antenna. Many of theseconfigurations will generally include a junction member disposed betweenand separating the proximal and distal radiating portions. As furtherdetailed herein, the devices and assemblies described here provide forreinforcement members of various configurations that are disposed withinthe junction members to further stiffen and strengthen the overallassembly, without compromising the functionality of the assembly or itsease of manufacture.

Antenna Assembly with Reinforced Junction Member

Generally, the antenna assembly 10 in FIG. 1 shows a variation whereproximal radiating portion 22 is located proximally of distal radiatingportion 20, with junction member 18 preferably located between theradiating portions. Shaft 14 may electrically connect antenna assembly10 via cable 15 to generator 28 and usually comprises a coaxial cablemade of a conductive metal that may be semi-rigid or flexible. Shaft 14may also have a variable length from a proximal end of radiating portion12 to a distal end of cable 15 ranging between about 1 to 10 inches. Theshaft may be constructed of copper, gold, or other conductive metalswith similar conductivity values, but shaft 14 is preferably made ofstainless steel. The metals may also be plated with other materials,e.g., other conductive materials, to improve their properties, e.g., toimprove conductivity or decrease energy loss, etc. A shaft 14, such asone made of stainless steel, preferably has an impedance of about 50Ωand to improve its conductivity, the stainless steel may be coated witha layer of a conductive material such as copper or gold. Althoughstainless steel may not offer the same conductivity as other metals, itdoes offer strength required to puncture tissue and/or skin. In manyvariations, the shaft will further include a cooling sheath thatsurrounds the coaxial cable, including but not limited to cooling sheathsystems described in U.S. Pat. No. 7,311,703, filed Jul. 18, 2003, whichis incorporated herein by reference in its entirety.

In operation, microwave energy having a wavelength, λ, is transmittedthrough antenna assembly 30 along both proximal and distal radiatingportions 36 and 38. This energy is then radiated into the surroundingmedium, e.g., tissue. The length of the antenna for efficient radiationmay be dependent at least on the effective wavelength, λeff, which isdependent upon the dielectric properties of the medium being radiatedinto. Energy from the antenna assembly 30 radiates and the surroundingmedium is subsequently heated. An antenna assembly 30 though whichmicrowave energy is transmitted at a wavelength, λ, may have differingeffective wavelengths, λeff, depending upon the surrounding medium,e.g., liver tissue, as opposed to, e.g., breast tissue. Also affectingthe effective wavelength, λeff, are coatings that may be disposed overantenna assembly 30, as discussed further below.

FIGS. 3A-3B show sectional views of radiating portion 12. As seen, theradiating portion 12 comprises proximal radiating portion 22 and distalradiating portion 20. Proximal radiating portion 22 may typically havean outer conductor 42 and an inner conductor 44, each of which extendsalong a longitudinal axis. Between the outer and inner conductors 42 and44 is typically a dielectric material 46, which is also disposedlongitudinally between the conductors 42 and 44 to electrically separatethem. A dielectric material may constitute any suitable dielectricmaterial, including air. Distal portion 20 is also made from aconductive material, as discussed below. Proximal and distal radiatingportions 22 and 20 align at junction member 50, which is typically madeof a dielectric material, as is further discussed below. As seen,junction member 50 has first and second junction mating sections 52 and54 that may be connected to distal and proximal portions 20 and 22,respectively. Junction member 50 is preferably comprised of any suitabledielectric material. Alternatively, a dielectric coating or layer mayalso be applied to the inside of channels 62 and 64 which contactjunction member 50. First and second mating sections 52 and 54 may bethreaded as shown by threads 56 and 58, respectively, such that thethread pitch on each section 52,54 is opposed to each other, i.e., thepitch angle of threading 56 may be opposite to the pitch angle ofthreading 58. Alternatively, the thread pitch on each section may beconfigured to be angled similarly for ease of antenna assembly. Distalportion 20 may have a receiving cavity or channel 62 which is threaded66 at a predetermined pitch to correspond to the pitch and angle of thethreading 66 on first mating section 52. Likewise, proximal portion 22may have a receiving cavity or channel 64 which is threaded 68 at apredetermined pitch to correspond to the pitch and angle of thethreading 58 on second mating section 54. Having opposed pitch anglesmay help to ensure a secure fit or joint when antenna assembly isassembled by screwing proximal portion 22 and distal portion 20 togetheronto junction member 50.

As can be seen, channel 60 extends axially through junction member 50and receives reinforcing member 70 which is generally cylindrical andconfigured to be received within and extend through the channel 60. Thereinforcing member is generally formed of a stronger and stiffermaterial than the junction member and thus reinforces the junctionmember. In the variation depicted the reinforcing member is integrallyformed with inner conductor 44 and includes central section 72 thatresides within junction member 50 and a distal section 74 that extendsfrom the junction member distally into the distal radiating portion.Wire 78 extends distally from section 74 and is in electrical contactwith the inner perimeter 21 of the distal radiating section 20. In thisconfiguration, the reinforcing member thus functions to extend the innerconductor through the junction member and into the distal radiatingsection. The combination of the inner conductor 44, reinforcing member70 and terminal wire 78 into a single piece has manufacturing andassembly advantages. The terminal wire 78 can be bent such that uponinsertion into the distal radiating portion, it comes into contact withthe perimeter 21. The piece can further include stop 76, which retainsreinforcing member 70 against junction member 50 and prevents it frommoving proximally relative to the reinforcing member. In alternativeconfigurations, the reinforcing member can be a separate piece thatallows for passage of the inner conductor through to the distal section.In such alternative configurations, the reinforcing member need not beelectrically conductive and in many configurations it may be desirablefor the reinforcing member to be formed of a dielectric material. Thismaterial, for example, may be chosen so as to retain optimal antennacharacteristics.

FIGS. 4A and 4B show another variation of a reinforced microwave antennaassembly. In this variation, reinforcing member 170 is again integrallyformed with inner conductor 144 and includes central section 172 thatresides within junction member 150. Junction member 150 is similar tojunction member 50 of FIGS. 3A-3B in that it includes threaded first andsecond mating sections 152 and 154, that are screwed on to internalthreads 166 and 168 of distal and proximal radiating sections 120 and122. Reinforcing member 170 also includes a distal section 174 thatextends distally from the junction member into the distal radiatingportion. Distal section 174 is threaded 176 at its terminal end. Distalradiating section 120 is formed of tapered distal tip 124 (althoughshown as tapered, it need not be so) and section 123 that each haveinternal threads 125 and 127, respectively, that are aligned to bothengage the threaded portion 176 of the reinforcing member, as shown.This allows the distal section 174 to be screwed into the distalradiating portion, which both provides for an electrical connectionbetween inner conductor 144 and distal radiating portion, as well asproviding for increased strength and rigidity to the distal radiatingportion.

FIG. 8 depicts another variation of a suitable antenna assembly, whichis similar in most respects to FIGS. 4A and 4B, except that it lacksthreaded first and second mating 10 sections adjacent to the junctionmember 550. In this variation, the antenna assembly is held together bythe distal and proximal threads. That is, distal section 556 is threaded552 at its terminal end. Similarly, proximal section 558 is threaded atits terminal end 554.

FIG. 5 shows a further variation of a reinforced microwave antennaassembly. In this variation, the entire distal radiating section 220 isintegrally formed with reinforcing member 270 and inner conductor 244.Reinforcing member 270 resides within junction member 250 with distalradiating section extending distally from reinforcing member 270.Junction member 250 includes threaded first and second mating sections252 and 254. Mating section 254 of junction member 250 is externallythreaded as shown, and is screwed on to internal threads 268 of proximalradiating section 222. Mating section 252, however, is internallythreaded and is screwed on to externally threaded section 266 ofjunction member 250. In addition to reinforcing junction member 250,this configuration provides for continuous electrical communication ofthe inner conductor to the distal radiating portion.

Antenna Assembly with Reinforced Junction Member and Thermocouple

FIGS. 6A-6C show yet a further variation of a reinforced microwaveantenna assembly. In this variation, reinforcing member 370 is similarto reinforcing member 170 of FIGS. 4A and 4B in that it also includes acentral section 372 that resides within junction member 350. Junctionmember 350 is similar to junction members 50 and 150 of FIGS. 3A-3B and4 in that it includes threaded first and second mating sections 352 and354, which are screwed on to internal threads 366 and 368 of distal andproximal radiating sections 320 and 322. Reinforcing member 370 includesa distal section 374 that extends distally from the junction member intothe distal radiating portion. Distal section 374 is threaded 376 at itsterminal end. Distal radiating section 320 is formed of tapered distaltip 324 and section 322 that each have internal threads 325 and 327,respectively, that are aligned to both engage the threaded portion 376of the reinforcing member, as shown. This allows the distal section 374to be screwed into the distal radiation portion, providing for increasedstrength and rigidity to the distal radiating portion. Unlikereinforcing member 170, however, reinforcing member 370 contains acentral channel 377 that receives and allows passage of inner conductor344 through junction member 350. As shown most clearly in FIG. 6B, innerconductor 344 extends the length of the assembly to its distal tip 324where it emerges from the assembly. Inner conductor 344 terminates inneedle tip 345. As also shown, the inner conductor is hollow, allowingpassage of thermocouple 380 which is positioned within the innerconductor lumen with thermocouple junction 382 at the tip. While tip 382is shown as rounded or blunt, it need not be. That is, tip 382 can haveany suitable geometry, e.g., it can be sharp, or have a piercing distaltip. In addition, thermocouple 380 may be slidable within the antenna,and may even be configured to extend out of the distal end of theantenna. Like the tip 382, the thermocouple 380 may have any suitablegeometry. For example, it can be configured, such that when it isdeployed out of the distal end of the antenna, it assumes a curvedconfiguration. The thermocouple can provide and monitor localizedtemperature readings of tissue when the device is operated. Othermonitoring devices can be deployed through the inner conductor lumen,including but not limited to sensors and transducers that respond to,e.g., electrical, magnetic, optical, thermal or mechanical stimulus. Theinner conductor lumen can also be used to deliver fluids, such asirrigation fluids, or therapeutics, or to remove tissue or fluidsamples. Additional thermocouples or other monitoring devices can alsobe provided. For example, as shown most clearly in FIG. 6C, thermocouple390 having thermocouple junction 392 is positioned proximal of proximalradiating section 322 in lumen 347 between outer conductor 342 and shaft314. Lumen 347 can contain e.g., a cooling fluid and thermocouple 390can be used to measure the temperature of such cooling fluid.

Antenna Assembly with Reinforced Junction Member and Cooling Chamber

FIG. 7 shows another variation of a reinforced microwave antennaassembly. In this variation, reinforcing member 470 is similar toreinforcing member 170 of FIG. 4A. Junction member 450 is also similarto junction member 150 of FIG. 4A in that it includes threaded first andsecond mating sections 452 and 454, which are screwed on to internalthreads 466 and 468 of distal and proximal radiating sections 420 and422. Reinforcing member 470 includes a distal section 474 that extendsdistally from the junction member into the distal radiating portion.Distal section 474 is threaded 476 at its terminal end. Distal radiatingsection 420 terminates with tapered distal tip 424 (although, as notedabove, in some situations, the distal tip need not be tapered).

A dielectric 446 is positioned longitudinally between inner conductor444 and outer conductor 448 to electrically separate them, In thisvariation, a cooling tube 456 is positioned longitudinally adjacent toouter conductor 448, and a cooling jacket 458 is positionedlongitudinally adjacent to cooling tube 456, making up a coolingchamber. While not shown if FIG. 7, the proximal end of the cooling tubeis connected to a source of cooling fluid. The cooling fluid passesthrough the cooling tube 456 (e.g., a polyimide tube or the like) tocool down the tissue immediately adjacent to cooling jacket 458 toprevent burning or other tissue damage. The cooling fluid may be anysuitable fluid (e.g., water, saline, etc.).

Materials and Methods

Junction members used in the antenna assemblies described herein arepreferably made of a dielectric material such as a ceramic or othersuitable dielectric. Illustrative examples of suitable dielectricmaterials include, but are not limited to Al₂O₃, Boron Nitride,stabilized Zirconia, air, and the like. Alternatively, junction memberscan made of a metal and sufficiently coated with a dielectric or polymer(e.g., high temperature polymers like polyimide or Ultem™ provided thedielectric coating is sufficiently thick to provide adequate insulation.To prevent energy from conducting directly into the tissue during use, adielectric layer having a thickness between about 0.0001 to 0.025 inchesmay be coated directly over the antenna assembly. The dielectric coatingmay increase the radiated energy and is preferably made from a ceramicmaterial, such as Al₂O₃, TiO₂, or the like, and may also be optionallyfurther coated with a lubricious material such as Teflon™,polytetrafluoroethylene (PTFE), or fluorinated ethylene propylene (FEP),etc. In addition to the dielectric coating, a sealant layer may also becoated either directly over the antenna assembly, or preferably over thedielectric layer to provide a lubricious surface for facilitatinginsertion into a patient as well as to prevent tissue from sticking tothe antenna assembly. The sealant layer may be any variety of polymer,but is preferably a thermoplastic polymer and may have a thicknessvarying from a few angstroms to as thick as necessary for theapplication at hand. The sealant layer may be made from a variety ofthermoplastic polymers, e.g., heat shrink polymers, such as polyethylene(PE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE),fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA),chlorotrifluoroethylene (CTFE), ethylene chlortrifluoroethylene (ECTFE),and ethylene tetrafluoroethylene (ETFE). Varying these coatingthicknesses over antenna assembly may vary the effective wavelengths,λeff, of the radiation being transmitted by the antenna. Thus, one mayvary the coating thicknesses over the assembly to achieve apredetermined effective wavelength depending upon the desired results.

A preferable method of optimizing the amount of radiated energy from theassembly may include adjusting the length of proximal radiating portionto correspond to a length of nλ/4 (where n is any integer) of theradiation being transmitted through assembly, and likewise adjusting acumulative (or overall) length of distal radiating portion and junctionto also correspond to a length of nλ/4. Adjusting the lengths ofproximal and distal radiating portions to correspond to the wavelengthof the transmitted microwaves may be done to optimize the amount ofradiated energy and accordingly, the amount of the medium or tissue thatis subsequently heated. The actual lengths of proximal and distalradiating portions may, of course, vary and is not constrained to meetany particular nλ/4 length. When an antenna assembly is radiatingenergy, the ablation field is variable 3-dimensionally and may beroughly spherical or ellipsoidal, which centers on the junction memberand extends to the ends of the proximal and distal radiating portions.

The location of the distal tip may be proportional to a distance of nλ/4of the radiation being transmitted through the assembly. However, sincethe distal tip typically terminates at tapered end, the angled surfaceof taper may be taken into account. Thus, the total distance along theouter surfaces of the junction member and distal radiating portion(including any tapered end) may accord to the distance of nλ/4. Thelength of proximal radiating portion may also accord to the distance ofnλ/4, as above. Although it is preferable to have the length of theradiating portion of the antenna accord with a distance of thewavelength, λ, it is not necessary for operation of the device, asdescribed above. That is, an antenna assembly having a radiating portionwith a length in accordance with a first wavelength may generally stillbe used for transmitting radiation having a second wavelength, or thirdwavelength, or so on, although with a possible reduction in efficiency.Also, while the variations described above are related to dipole antennaassemblies, monopole antenna assemblies are also contemplated.

To improve the energy focus of an antenna assembly, an electrical chokemay also be used to contain returning currents to the distal end of theantenna, as is described in U.S. patent application Ser. No. 10/052,848filed Nov. 2, 2001, now U.S. Pat. No. 6,878,147, which is incorporatedherein by reference in its entirety. Generally, the choke may bedisposed on the antenna proximal of the radiating section. The choke ispreferably placed over a dielectric material, which may be disposed overthe antenna. The choke is preferably a conductive layer and may befurther covered by a tubing or coating to force the conductive layer toconform to the underlying antenna, thereby forcing an electricalconnection (or short) more distally and closer to the radiating section.The electrical connection between the choke and the underlying antennamay also be achieved by other connection methods such as soldering,welding, brazing, crimping, use of conductive adhesives, and the like.

Additional steps may optionally be taken to further increase thestrength of an antenna assembly by altering any of the layers, such assealant layer or any of the other heatshrink layers discussed above.Wires or strands may be formed within, or on, the layers to add strengthand are preferably orientated longitudinally along the length of theantenna such that the bending strength of the antenna is increased. Thelayers may be formed over the outer conductor, as described above, andthe wires may be made of any high-strength material, e.g., Kevlar,metals, etc. Metal wires may be used, provided they are insulated.

Antenna Deployment

As described above, the microwave antenna may be inserted directly intothe tissue and into the lesion to be treated. However, during insertion,the antenna may encounter resistance from some areas of tissue,particularly in some tissue found, e.g., in the breast. When themicrowave antenna encounters resistance, if force were applied, tissuedamage may result or the target tissue may be inadvertently pushed awaydue to the differential density of the target tissue relative to thesurrounding tissue. Therefore, RF energy may also be utilized with themicrowave antenna for facilitating deployment within the tissue.

In use, the RF energy may be simply left on the entire time the antennais advanced through the tissue, or it may be applied or turned on onlyas needed as the antenna encounters resistance from the tissue. With theRF energy activated, the antenna may be further advanced utilizing theRF energy to cut through the obstructive tissue. Once the antenna hasbeen desirably positioned within a lesion or region of tissue, the RFenergy, if on, may be switched off and the microwave energy may beswitched on to effect treatment.

In certain variations, the assembly may use RF energy at the distal tipof the antenna as a cutting mechanism during antenna deployment. Themicrowave antenna is preferably covered with some insulative materialalong most of its length, but distal tip may be uninsulated such thatthe FW energy may be applied thereto through the inner conductor. Toutilize the RF energy cutting mechanism at the distal tip, the innerconductor may be made from Nitinol, Tungsten, stainless steel, or someother conductive metal.

The antenna assembly may be electrically connected to an RF generatorthat provides the RF energy to the distal tip during placement andpositioning of the antenna within the tissue or lesion. After theantenna has been desirably positioned within the lesion, the connectormay be disconnected from the RF cable and attached to a microwavegenerator via a microwave cable to provide the microwave energy foreffecting treatment to the tissue.

Alternatively, given the small amount of surface area of the distal tipof the assembly, a low power FW generator may be utilized and can bebuilt into an integral unit along with the microwave generator.Alternatively, an optional RF generator may be physically separated fromthe microwave generator and may be electrically connected as a separateunit to the antenna.

Aside from the illustrations of possible antenna deployment methods anddevices described above, other variations for deployment and insertioninto tissue may be utilized. Potential other methods and devices forantenna deployment and insertion may be found in U.S. Pat. No.7,197,363, filed Sep.. 15, 2002, which is commonly owned and isincorporated herein by reference in its entirety.

Methods of Use

In using a microwave antenna, several different methods may be utilized,including the use of single or multiple antennas, as is furtherdescribed U.S. patent application Ser. No. 10/052,848 filed Nov. 2,2001, now U.S. Pat. No. 6,878,147, which is incorporated herein byreference in its entirety.

The applications of the antenna assemblies and methods of making theassemblies discussed above are not limited to microwave antennas usedfor hyperthermic, ablation, and coagulation treatments but may includeany number of further microwave antenna applications. Modification ofthe above-described assemblies and methods for carrying out theinvention, and variations of aspects of the invention that are obviousto those of skill in the art are intended to be within the scope of theclaims.

What is claimed is:
 1. A microwave antenna assembly, comprising: aradiating portion configured to operably couple to a source of microwaveenergy, the radiating portion including: a proximal radiating portionincluding: an outer conductor; an inner conductor disposed within theouter conductor; and a dielectric material disposed between the outerand inner conductors; and a distal radiating portion disposed distallyof the proximal radiating portion, the inner conductor extendinglongitudinally within the distal radiating portion; a lumen formedaround the outer conductor and configured to receive cooling fluidtherein; and a thermocouple disposed within the radiating portion andconfigured to sense temperature within the radiating portion.
 2. Themicrowave antenna assembly according to claim 1, further comprising atemperature sensor disposed within the lumen and configured to sensetemperature of the cooling fluid.
 3. The microwave antenna assemblyaccording to claim 1, wherein the thermocouple includes a blunt distaltip.
 4. The microwave antenna assembly according to claim 1, wherein thethermocouple extends distally at least partially along a longitudinallength of the radiating portion and terminates in a thermocouplejunction.
 5. The microwave antenna assembly according to claim 1,wherein the thermocouple is at least partially disposed within the innerconductor.
 6. The microwave antenna assembly according to claim 1,further comprising a junction member disposed between the proximal anddistal radiating portions, the inner conductor extending longitudinallythrough the junction member.
 7. The microwave antenna assembly accordingto claim 6, further comprising a reinforcing member disposed within thejunction member, wherein the reinforcing member is more rigid than thejunction member.
 8. A microwave ablation system, comprising: a source ofmicrowave energy; and a microwave antenna assembly including: a proximalradiating portion configured to be operably coupled to the source ofmicrowave energy, the proximal radiating portion including: an outerconductor; an inner conductor disposed within the outer conductor; and adielectric material disposed between the outer and inner conductors; anda distal radiating portion disposed distally of the proximal radiatingportion, the inner conductor extending longitudinally within the distalradiating portion; a lumen formed around the outer conductor andconfigured to receive cooling fluid therein; and a thermocouple disposedwithin at least one of the proximal or distal radiating portions andconfigured to sense temperature within the at least one of the proximalor distal radiating portions.
 9. The microwave ablation system accordingto claim 8, wherein the antenna assembly further includes a temperaturesensor disposed within the lumen and configured to sense temperature ofthe cooling fluid.
 10. The microwave ablation system according to claim8, wherein the thermocouple includes a blunt distal tip.
 11. Themicrowave ablation system according to claim 8, wherein the thermocoupleis disposed distally of a distal end of the inner conductor.
 12. Themicrowave ablation system according to claim 8, wherein the thermocoupleis at least partially disposed within the inner conductor.
 13. Themicrowave ablation system according to claim 8, wherein the antennaassembly further includes a junction member disposed between theproximal and distal radiating portions, the inner conductor extendinglongitudinally through the junction member.
 14. The microwave ablationsystem according to claim 13, wherein the antenna assembly furtherincludes a reinforcing member disposed within the junction member,wherein the reinforcing member is more rigid than the junction member.